The purpose of this study is to investigate how mild, noninvasive electrical brain stimulation affects speech relevant brain areas, which may in turn affect speech fluency and speaking-related brain activity in people that stutter. The long-term goal of this study is to test the therapeutic potential of transcranial alternating current stimulation (tACS) for the treatment of stuttering.

The study team hypothesizes that if stuttering involves impaired initiation of motor programs, delta-tuned tACS will strengthen communication between brain regions and decrease stuttering. Therefore, delta-tuned sensorimotor tACS will be paired with fluency-induced speech (choral reading), which is hypothesized to decrease stuttering via improved auditory motor integration.

Participants will have screening and baseline visits that include a variety of tests and procedures (i.e. standardized tests of speech, language, hearing test, music training questionnaire, working memory tests, and speech sample to characterize stuttering, magnetic resonance imaging (MRI) and electroencephalography (EEG)). Following these, participants will have 3 sessions (active and sham conditions) and then a one month follow-up phone or video call.

Of note, there will be an embedded pilot study to refine the experimental protocol in terms of practicality and feasibility and these participants will not be included in this registration. The only purpose of this embedded study is to refine the protocol and it does not have any health or behavioral outcomes.

Inclusion Criteria for stutterers:

• Have normal language, hearing, and cognition
• Speak English as the primary language
• Currently stutter
• Score (per protocol) a certain value on the Stuttering Severity Instrument (SSI-4).
• Have not received any treatment for stuttering within the past year

Exclusion Criteria for stutterers:

• History of seizures
• Major medical or neurological illness (e.g., stroke, serious head trauma, brain infection, Parkinson's disease, etc.)
• History of closed head injury with loss of consciousness (e.g., concussion)
• Metal or electronic implants such as cochlear implants and pacemakers anywhere in the body
• Braids or other hair styling that prevents direct access to the scalp (if removal not possible)
• Currently pregnant

Please note that because the most logical interventional study model is a single arm study the study team can't select a masking option. Please note that Participants, Investigators, and Outcomes Assessors will be blinded to active vs. sham stimulation (with the exception of one study investigator that pre-configures the randomization schedule, and this person will not be involved in any assessments/outcomes).